Satguru Sri Guru Gobind Singh Sahib ji Maharaj and Sri Vaheguru Ji Maharaj are one and the same, as you have said. In the lines you and jsinghz are discussing, Guru Sahib is showing people many things.
1. Guru Sahib is being humble.
2. None of our Gurus called themselves equal to Sri Vaheguru Ji Maharaj. However the next Guru didn't hestitate to say before, me the Guru is one and only Sri Vaheguru Ji Maharaj.
3. Guru Sahib in Dasam Bani states, i don't know all, only you (Sri Vaheguru Ji Maharaj) know all, again Guru Sahib is showing humility. If we take these lines literally, then how can Satguru Sri Guru Gobind Singh Sahib ji Maharaj be the True Guru. Gurbani tells us that the True Guru knows Sri Vaheguru Ji Maharaj. So there is a deeper meaning to the lines. When the Gurus wrote about themselves, they wrote with the utmost humility to teach us a lesson. Not to speak in ego about ourselves (Sikhs).
4. Also, so we don`t start worshipping Satguru Sri Guru Gobind Singh Sahib ji Maharaj as a devta (separate from Sri Vaheguru Ji Maharaj as the other religions do). Satguru Sri Guru Gobind Singh Sahib ji Maharaj told us don`t see any difference between me (Satguru) and Sri Vaheguru Ji Maharaj.
Satguru Sri Guru Gobind Singh Sahib Ji Maharaj is Sri Vaheguru Ji Maharaj!!!